I am interested in doing the same thing. I found the post below doing a search on VSS. Note I have not actually performed the VSS replacement, but the instructions below look good to me. Although I don't relish doing this on my back with the car up on ramps. I guess I'll try and replace the O2 sensors at the same time, since one of them is in the same vicinity. To get to the VSS from the top I think you'll have to sprawl across the intake mainifold.
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You definetly don't have to have the tranny out to do this. To find it just follow the speedometer cable down to the tranny housing and that's it. It is what the speedometer cable plugs into. The speedometer is held in by a pin that you just pull out.
Please note: The instructions that I am going to give you will give you an idea, but you do not have to remove the Y pipe. If you take off the intake it will be easier getting to it from the top. Also note that these instructions are for an AX4S, but all the ATX's have the VSS located in the same place. On the MTX-IV It's even easier, just look at your thermostat housing. The VSS is 6" closer to the firewall and down.
quote:
Vehicle Speed Sensor (VSS)
AX4S Trans axle
Removal
Raise vehicle on a hoist. Refer to Section 00-02.
Remove Y-pipe and heated oxygen sensors (HO2S)(9F472) from the exhaust system.
Remove VSS exhaust heat shield.
Remove bolt retaining VSS mounting clip to transaxle.
Remove VSS and driven gear from transaxle.
Disconnect electrical connector and speedometer cable from VSS. NOTE: Do not attempt to remove spring retaining clip from driven gear with speedometer cable in VSS.
Remove driven gear retainer and driven gear from VSS. Installation
Position driven gear to VSS.
Install gear retainer.
Connect electrical connector to VSS.
Ensure internal 0-ring is seated properly in VSS housing. Snap speedometer cable into VSS housing.
Install VSS into transaxle and secure with retaining bolt.
Install VSS exhaust heat shield.
Install Y-pipe and heated oxygen sensors to exhaust system.
Lower vehicle and verify proper speedometer I odometer operation.
Let me know if you guys need any more info.
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Mike Kopstain
Midwest SHO Specialists
[email protected]